A washing machine washes laundry using the surfactant action of detergent, a water stream generated via rotation of, for example, a washing tub or a washing blade, and shocks applied by the washing blade. The washing machine may perform washing, rinsing and/or dehydration processes to remove contaminants in laundry or clothes through an interaction of water and detergent. A washing machine may include a casing defining an appearance of the washing machine, an imperforated tub, which is provided in the casing in a suspended state, and a perforated basket or a drum, which is rotatably provided in the tub. Since the basket and the tub may become contaminated due to various causes, such as, e.g., scaling, slime, solidified detergent, with repeated use over a long time, periodically cleaning the tub and components provided in the tub, or tub washing, may remove the contamination sources.
Although a washing machine may provide an additional tub washing operation, which may be executed when selected by a user, it may not be easy to determine a time when the tub washing may be necessary. Furthermore, although the tub washing operation may be unrelated to an actual washing of laundry, execution of the tub washing course may consume considerable amounts of time, water and electricity, thereby making it difficult to utilize the tub washing operation. Consequently, laundry may be contaminated by pollutants from a basket or a tub, and such contamination may be dissatisfactory to users.